Landing gear for aeroplanes



- Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE LANDING GEAR nonAnnormnns Robert S. Waugh, Alhambra, and Whitman Reed, Huntington Park,Galit, assignors, by

mesne assignments, ,to The Cleveland Pneumatic Tool Company, Cleveland,

notation of Ohio Ohio, a corapplication May 11, 19:1; sci-mun. 536,566

3 Claims. (CL 267-64) The present invention contemplates the provisionof a shock absorbing unit'adapted to be interposed between the runninggear and rthe fuselage of -an aeroplane and within which uniti isincorporated fluid and hydraulic-compression means for dissipatingimpact energy delivered to the plane; as well as resisting recoil force.

The invention is illustrated by way of example in the accompanyingdrawing in which:

Figure 1 is a view in front elevation showing an aeroplane equipped withthepresent inven- 'tral vertical section showing the-modified form" ofthe invention in which a choke pin is incr-- porate'd.

Fig. is a detailed view, partly in section, of a'portion ofthe-structure illustrated in Fig. 4, with the valve in the positionwhich it occupies upon the impact stroke.

Referring more particularly to the drawing, l0

indicates the wing structure of an aeroplane here shown as mounted upona fuselage H and suitably held by reinforcing struts 2. Appropriatelypositioned at the opposite sides ofthe fuse lage are landing wheels l3and it here shown: as provided with forks l5, which extend verticallyand have a center shaft l5 directly connected with one element of alanding gear shock absorber ll, with which structure the presentinvention is particularly concerned. The shock .absorbin'giinit isrigidly secured to the sides of the fuselage by fastening members 18.These members are formed integral with or secured to the wall of anupper cylinder l9 which has a pertainsto a landing gear closed upper endII and a downwardly proiec lug cylindrical body substantially uniformindiameter, and the lower end of which is closed byapackingwall 2iwhichisexternallythreaded and is screwed into the mouth of the cylinderl9. 5

The packing wall 2! is formed with a central opening 22 through which a.lower cylinder 23 extends andreciprocates. This lower cylinder-istubular and projects upwardly to terminate in an externally end which isscrewed into the central bore of an upper piston '24. The piston isformed with a counterbore portion 25 in communicationwith the interiorof the tubular lower cylinder 23 and whlchterminates at its upper end ina cylindrical opening 2 through -which a check tube 21 extends andreciprocates.

The check tube Z'Iis tion to the upper cylinder is and is held in rigidrelation to this cylinder by a threaded screw 28 formed as.a-contim1atlon of its upperend and passing through the cylinder wall 20whereit is held by a nut 29. Theouter piston 24 is provided with a cuppacking 30 and.a special arrangement of labyrinth packing ll which willprevent interchange of fluid around the outer piston 24 and between theupper compartment 32 of the upper cylinder i9 and the lower compartment33 of the same cylinder.

The check tube 21 is of a diameter considerably smailer than thecounterbore 25 in the piston 24 and the inside diameter of the lowercylinder 23, thus forming a liquid compartment 34 around the check tube21 and within the space defined by the wallof the coimterbore 25 and thewall of the lower cylinder 2:. The lower 35 end of the compartment 3| isdefined byan inner piston ,35 which is in the shape of a cylindricalcapscrewed on to the lower end of the check tube 2! and thus accommodates adisc. shaped valve member so which is mounted within the inner piston 35and may oscillate for a distance determined by the thickness of thevalve' member 38 and a distance between the upper face of the end 31 ofthe piston and the lower face of the check tube 21. A bypass opening 39is'formed in the ,end wall 31 and a plurality of bypass openings 40 areformed through and are distributedaround the cylindrical portion 36of'the inner piston 35.

Attention is also directed to the fact that the to gradually settle asthe shockabsorber is dis tended and while H the load been removedtherefrom.

The lower cylinder 23 and the portion of the compartment 32 in the uppercylinder 19 are filled with an incompressible fluid such as oil, whichfluid may be drained from the device by the removal of a drain plug 42disposed at the lower closed end of the lower cylinder 23. The portionof the compartment 32 in the upper cylinder l5 which is not filled withliquid is filled with a fluid under pressure, such for example as airdelivered through the air valve 43. The compartment 33- beneath thepiston 24 and within the cylinder l9 may be supplied with oil through agrease unit 44, and. is also provided with a breather duct 44'.

--.In the construction as shown in Fig; 4 of the drawing, a difierentform of inner piston is provided,'as indicated at 45.'- This piston isshown as comprising a reciprocating sleeve 46 intowhich the lower end ofthe check tube 21 extends, and which sleeve is mounted to have limitedreciprocation with relation to the tube. Bypass cpenings 41 are formedthrough the side wall of this sleeve and may move toregister withsimilar openings 48 formed in the tube 21, at whichtime fluid may passthroughthe sleeve 46, and the tube 21, and from the lower cylinder 23into the check tube 2L The lower end of the piston 45 is fitted with aremovable threaded wall structure 49 having a central openingiflth'erethrough. Extending through this central opening is, a taperedchoice pin 5l which will coop mte'withlthe open-- ing 50 in the pistonto progressively vary the efi'ective passageway through the opening 50and from the lower-cylinder 23 into the' piston 45. As an emergencyprovision a helical spring 52 is provided for the purpose of preventingcome plate collapse of the shock absorber unit ifthe fluid leaks fromit, as might be the casein warfare, and in which event the cylinders ofthe shock absorber might be punctured by a projectile. The 1 spring 52is secured in the upper end of the upper cylinder l3 and extends downaround the check tube 21 for a distance. The lower end of the springwill be encountered by the upper face of the piston 24 under extremetelescoping condi -'tions of the cylinders.

In operation of the present invention the shock absorbers are assembledas shown in the drawing,

with the vertical spindle is rigidly secured within A the sockets s: atthe lower ends or the lower cylinders 23. It willtherefore -be evidentthat these spindles may rotate around the vertical axes as occasion mayrequire, having a castorefiect. When the shock absorbers are-thusassembled, a desired quantity of liquid is placed in them,

-aIter which air to a desired pressure is introduced through .theairvalve 43. When the areoplane' leaves the ground the weight of thewheels l3 and their forks l5will pull downwardly on the lower cylinders23, drawing the lower cylinder out oi the upper cylinder -until-the.lower face of the piston 24 strikes 'the endwall 2! of the uppercylinder, or until the fluid within thecompart-- meat 33 has'acted toresist further downward movement of'the lower cylinder 23 under influ-.ence of the weight of the wheel. This condition is illustrated in Fig. 2of the drawing. When the aeroplane is landed its wheelswill normallyfirst strike the ground and-force upwardly on the lower cylinder 23,simultaneously telescoping the lower cylinder 23' intothe upper cylinder24 and forcing the checktubefl downwardlyintothelower cylinder 23. Theact of forcing the lower cylinaosarac dei- 23 upwardly into the cylinderi3 will cause the piston 24 to force against the incompressible causethe air within the compartment 32 to be fluid in the bottom of thecompartment :2. and

proportionately compressed. At the same time 5 the inner piston 35 willbeforced downwardly into the incompressible fluid within the lowercylinder 23, raising the disc valve 35 to the position illustrated inFig. 3, permitting liquid to pass through restricted opening 35, in thepiston'and l0 restricted openings'38 in the valve, and thus into thecheck tube. At the same time, the passage of liquid from the cylinder 23into the annular chamber-34 is facilitated, because liquid mayance-space 4| around. .the periphery of the piston 35. When weight ofthe aeroplane has been completely imposed upon the shock absorbers andthe landing force has been absorbed, it will be evident that the air inthe compartment 32 oi the cylinder It will be under compression and willact to provide a pneumatic cushion for the aeroplane while ittaxies'a'cross the field. In

. then flow througfi opening 39 and through bypass 15 openings 40,aswell as throughthe .annular clearthe event that the cylinder 19 shouldspring a leak the compression of the air will be lost and the outer andinner cylinderswould be telescoping until the upper face or the piston24 would encounter the lower end of the spring 52, after which theaeroplane would be resiliently supported by the/sprin s, while ittaxies.

On the rebound stroke the disc valve 33 will 1 of course seat itselfupon piston 35, thereby closing ofl the openings 39 and 33! as indicatedin tube 21 back into the cylinder 23, the only path of flow thenavailable beingthrough the openlugs 45 and the annular clearance 4!around the I peripheryof the Piston 35. This position-otthe valve piece33 also serves to check the .flow of liquid out of the annular chamber34 into'the cylinder 23, because at this time the path of flow out ofthe annular chamber through openings 43 and is cut ofl. s

In the form of the invention shown in Fig. 4, 45

the rebound stroke the valve piece 45 takes the full line position,limiting the flow out of the Fig. 2 and checking the flow of liquid outof the 35 annular chamber around the check tube to the path provided bythe clearance surrounding the valve piece 45. The action of this form ofthe invention is therefore similar to that of Figs. 2 and 3 except thatthe communication between the cylinder 23 and the tube 21 changesprogressively on the compression and rebound strokes, and except thatthe communication between the cylinder 23 and the annular space aroundthe check tube changes progressively on the compression strokebut not onthe expansion or rebound 7o stroke.

Itwill thus be seen that the structure here disclosedj provideshydraulic means for normally receiving and absorbing impact" landingforce;-

and pneumatic means lorfabsorbing. minor vibra-' tion and impulsesincident to the travel of the plane along the ground.

While we have shown the preferred form of our invention, as now known tous, it will be understood that various changes may be made incombination, construction, and arrangement of parts by those skilled inthe art without departing from the spirit of our invention as claimed.

Having thus described our invention what we claim and desire to secureby Letters Patent is:

1. In a hydropneumatic strut, a pair of telescoping cylinders, the innercylinder carrying a piston slidabiy contacting with the outer cylinder,a metering pin carried by one of said cylinders and a check tube carriedby the other of said cylinders, said pin being concentric with saidtube, and a partial closure for the inner end of said tube surroundingsaid pin, whereby the flow of incompressible fluid into and out of saidtube is restricted, said tube carrying a valve opening into the innercylinder which closes on the rebound stroke.

2. In a'hydropneumatic strut, a pair of telescoping cylinders, the irmercylinder carrying a piston slidably contacting with the outer cylinder,a metering pin carried by one of said cylinders and a check tubeattached at one end to the other of said cylinders, said pin beingconcentric with said tube, and a partial closure for the inner end ofsaid tube surrounding said pin. whereby the flow of incompressible fluidinto and out of said tube is restricted, said tube carrying at its freeend a. valve which closes on the rebound stroke.

3. In a hydropneumatic strut, a pair of upstanding telescopingcylinders, the inner cylinder carrying a piston slidably contacting withthe outer cylinder, 2. check tube carried by the upper of said cylindershaving communication at its lower end through said piston with the lowercylinder, means for varying the effective size of said communicationduring a given stroke as the stroke progresses, and a valve carried bysaid check tube opening on the compression stroke and closing on theexpansion stroke for. facilitating the flow of liquid through the tubeon the compression stroke only.

WHITEMAN REED. ROBERT S. WAUGH.

